20 CHARACTERS OF AN EPIZOOTIC DISEASE 



infectious or epizootic disease except in the nature of the in- 

 vading organism. The lesions may vary and usually they do 

 especialh' in different species of animals. If a man receives 

 accidentally a cut from a knife with which he is making a post 

 mortem on an animal dead from anthrax, the lesion is liable to 

 be restricted to the point of inoculation, and while it is anthrax 

 (malignant pustule) it would very often be recognized as a 

 simple wound infection. If this accidental inoculation should 

 occur in a guinea pig, the disease would not be recognized 

 as a local lesion ; but the animal would most likely die of 

 septicaemia (§2). 



As a class, the lesions known clinically as wound infections 

 are differentiated from the specific diseases in a number of ways. 

 The bacteria commonly found in wound infections do not pro- 

 duce the epizootic diseases, although there are notable excep- 

 tions. x-Ygain, there is usually a difference in the mode of in- 

 fection. The virus of the epizootic disease is ordinarily intro- 

 duced through the digestive or respiratory tract or by means 

 of insects, while in wound infection the virus is introduced, as 

 the term implies, through the injured integument or mucosa. 



§ 14. The differential characters of a specific infec- 

 tious or epizootic disease. It is very important not to mis- 

 take for an infectious disease some form of body disturbance 

 due to a local cause or condition. Animals often suffer from 

 improper food and the conditions of life under which they are 

 compelled to live. It frequently happens that as all of the 

 animals in a given herd are subjected to like conditions, a 

 number of them, perhaps all, will manifest very similar symp- 

 toms and more or less of them die. Such an occurrence often 

 gives rise to the supposition that the cause of death is some 

 form of infectfon. Deaths from such causes or under such 

 conditions, should be carefully distinguished from an epizootic. 

 In differentiating a non-infectious disorder from a specific dis- 

 ease, it is important and usually sufficient to take into account 

 the appended characteristics of an infectious disease. 



(i) An infectious disease is caused by a specific agent. 

 This necessitates as the first requisite an exposure to and an 

 infection with the specific organism or etiological factor. 



